1. Field of the Invention
This invention relates generally to ground proximity warning systems, and more particularly, to a ground proximity warning system for aircraft of the type that provides warnings for an excessive descent rate of an aircraft for a particular altitude above ground at which the aircraft is flying. An advisory is also provided when an excessive descent rate condition exists and the aircraft is flying over mountainous or undulating terrain.
2. Description of the Prior Art
Ground proximity warning systems, including ground proximity warning systems that provide warnings when the descent rate of an aircraft is excessive for the particular altitude above ground at which the aircraft is flying are known. Typical systems that provide a warning when the descent rate is excessive are disclosed in U.S. Pat. Nos. 3,947,808; 4,060,793; and 4,215,334. All of the above-mentioned patents are assigned to the same assignee as the assignee of the present invention, and are incorporated herein by reference.
While the warning systems described in the above-mentioned references do provide satisfactory performance in most situations, there are some situations that require consideration. For example, in some situations, the aircraft may be intentionally placed into a rapid descent condition to avoid a missed approach. This situation typically occurs when an aircraft is on approach and is at too high of an altitude above ground for the distance at which the aircraft is from the airport. Thus, the pilot may try to avoid missing the approach by descending at a descent angle which would cause an excessive rate warning. Maneuvering in this manner to avoid a missed approach may be safe if the pilot is on a visual approach and can see the runway, or if the pilot is on an instrument approach, and the descent angle is not too steep and sufficient terrain clearance exists. Such a maneuver may cause a SINK RATE warning to be generated even though th4e maneuver is safe.
However, certain other factors must also be considered, for instance, a navigational error or pilot error. When an aircraft is intentionally placed into a condition of excessive descent rate by the pilot to avoid missing an approach, the pilot will be cognizant of this fact and will ignore Sink Rate warning. This is not a problem if the aircraft is on the correct approach, but if due to navigational or pilot error the aircraft is off course, ignoring the warning may result in impact with terrain before the pilot has a chance to react. Thus there exists a need to provide a warning system which provides satisfactory warning to the pilot in such a situation, particularly when the aircraft is flying over undulating terrain.